The present invention relates to a removal method for water-soluble macromolecular compounds. Specifically, the present invention relates to a method for removing water-soluble high molecular weight compounds, wherein cationic, anionic, or amphoteric water-soluble macromolecular compounds are removed from an aqueous solution without affecting the quality and yield of other components in the solution. More specifically, the present invention relates to a method for removing water-soluble high molecular weight compounds, particularly flocculants, from aqueous solutions containing fermentation products. This method does not reduce the activity or the recovery yield of fermentation products, and completely removes excess macromolecular flocculants in the solution.
Water-soluble high molecular weight macromolecular compounds are used industrially in a variety of fields. These compounds are useful as flocculants and dehydrants in waste water treatment, as yeast-separating agents in fermentation production processes, as scale-preventing agents for cooling water systems, and as drainage aids in paper production processes. However, if these compounds are not removed from the solution, problems such as increased environmental pollution and decreased product quality can arise. In other instances, adherence of the macromolecular compounds to pipes or membranes may result in decreased processing efficiency. As a result, it is often desirable to remove the water-soluble macromolecular compounds from the aqueous solution.
When producing valuable substances by fermentation, such as enzymes and the like, yeast cells used in production are typically separated from the fermentation products by solid-liquid separation techniques, such as membrane filtration or centrifugation. Macromolecular flocculants are used to aggregate the yeast cells, and the aggregated yeast cells are then separated from the fermentation products which remain in solution. However, these separation techniques often leave excess macromolecular flocculant in solution. The residual macromolecular flocculent can mix with the fermentation products and reduce the quality of the product. Alternatively, the excess flocculent may adhere to membranes or ion exchange resins used in subsequent purification of the fermentation products, causing a marked decrease in performance.
Various methods have been proposed for removing water-soluble high molecular weight compounds from solution. For example, in Japanese Patent Publication Number Sho 54-2992, a method is proposed wherein an anionic surfactant is added to waste water containing a cationic macromolecular flocculent, thereby generating a water insoluble compound. In Japanese Patent Publication Number Sho 50-51467, there is proposed a method wherein metallic salts such as aluminum salts and iron salts are added during coagulation processing of a suspension. The amount of macromolecular flocculant which leaks out is thereby minimized. In Japanese Patent Publication Number Sho 50-56365, there is proposed a method wherein metallic salts, such as aluminum salt or iron salt, and a macromolecular flocculent are used jointly for the coagulation processing of a suspension. First, metallic salt is added, and thereafter macromolecular flocculant is added before the formation of a metallic hydroxide is completed. In this fashion, the amount of macromolecular flocculant which leaks out of the complexes and reenters the processed water is minimized.
These methods apply only to either an anionic macromolecular flocculant or a cationic macromolecular flocculent. Consequently, amphoteric water-soluble macromolecular compounds cannot be used. Furthermore, if metallic salts or surfactants are added to a fermentation solution containing enzymes, the activity of the fermentation products may lowered. As a result, in the prior art it was not possible to have a single method for efficient removal of water-soluble macromolecular compounds used in various industrial processes.